Automatic telephone system



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AUTOMATIC TELEPHONE SYSTEM Original Filed Dec. 12, 1924 2 Sheetsnsheet 12 `Patented vJuly 9, 1929.

lUNITED STATES PATENT OFFICE.

JOHN E. OSTLINE, 0F LIVERPOOL, ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

. Application led December 12, 1924, SeriatNo. 755,374, and in Great Britain January 1, 1924. Renewed March 28, 1929.

The present invention concerns im rovements in or relating to the extension ot automatic telephone systems to large networks which are originally purely manual, but at the same time it should be understood that certain of the features are applicable to telephone systems generally. More particularly the invention relates to telephone systems employing register senders and the principal object of the present invention is to provide a system which will enable a conversion of large networks from manual to automatic working to be effected in a most economical manner' consistent with meeting all the requirements of the transition stages and the ultimate conditions. A principal feature of the present invention is the arrangement whereby loop :irn-4 pulses generated loy the register sender alone can control the operation of automatic switches. This avoids the use of repeaters between exchanges interconnected by direct trunk lines andenables the, construction of the repeaters required to be considerably simplitied, consequently a further feature of the present invention is the provision of special repeaters to meet these conditions.

Further in order that the calling party cannot control the switches under any conditions while at the same time enabling the meteringr arrangements to be. simplified, battery feed for the calling party is fed from the first se,- lector. clude means for preventing impulses being generated whenever a. secondary non-numerical switch is seized until the next numerical switch is seized and also for enabling a register sender to exert a dilferent controlling elicct according to the. route over which it is seized. both these features being conveniently eti'ected by a polarized relay responsive to a reversal of current over the talking or impulsing conductors.

Another feature of the invention concerns a register sender adapted to be readily modified so as to enable the. register switch to be used either in a three or two digit system, that is a system employing either two or three digits for selecting the required exchange.

Another feature ot the' present invention concerns improved arrangements for transmitting aclistinctive tone to the calling party Other features of the invention in-v should he delay to dial after removing his receiver or after dialling an incomplete number.

Still another feature of the present invention concerns an improved impulsing circuit 1n which two impulsing relays in different swltches are arranged to he controled over a calling partys loop circuit, in su h manner that both relays may energize in series with the calling partys loop during the setting u p of a connection or one may be deenergized by short circuiting it at the switch with which the other relay is associated.

These and further features not specifically mentioned above, but set forth in the accompanying claims, will he understood by referring to the accompanying drawings comprlsing Figures l to 12 inclusive, in which Fig. l is a trunking layout of the system which is shown in detail in Figs. 2 to l2, inclusive.

Figs. 2 to 12, inclusive, are circuit diagrams of sufficient of the apparatus used in a complete director system to illustrate the preferred form of the invention.

rlhe' line of the automatic substation A, Fig. 2, terminates at the exchange in the line switch LS. The line switch LS has access to a number of trunk relay groups such as TR, each of which is individual to an exchange selector such as ES. There is a secondary line switch associated with each trunk relay group and the. secondary switch SLS has access to a number of director selectors DS, Fig. 3, which in turn have access to a number of directors` one. of which is shown in Figs. 4- t, inclusive. The line switch LS, Fig. 2'is mechanically of the well known rotary type having however, improved and novel arrangements for restoring its wipers to normal or home position and air improved and novel metering circuit.

The line switches LS1, LS2, LS3. LS, and LS5 are similar to the line switch LS. The sccondamv switches SLS, SLS1 and SLS2 are also similar to the line switch LS except that their controlling relays are located in the trunk relay groups and are adapted to control other circuits. The seconda-ry switch SLS3 is mechanically of the well known rotary type in which the wipers have no normal position and move in a forward direction only.

The exchange selector ES is a two motion vertical and rotary switch mechanically of the well known type and has its bank contacts arranged in horizontal rows pr levels. The exchange selectors ES1-ES", inclusive, the exchange selector CES, the selectors S-S, inclusive, and the connectors FSFS3, inclusive, are of the same type of switch mechanically.

The repeater R is an impulse and busy flash repeater of novel type for manual or automatic to automatic inter-exchangeworking. The repeaters R2 and R3 are provided for use in automatic to manual inter-exchange working and are adapted to transmit a s cial holding current back to hold up switc es independently of the calling party. 'lhe repeater R is a special repeater forvv use in connection with calls from an automatic to a manual exchange having a call indicator equipment and in itself forms no part of the piesent invention.

The complete director illustrated in Figs. 4-6, inclusive, comprises essentially the master di 't switch MDS, the B and C digit register CR, Fig. 5, the sender control switch SCS and the digit revisters DRl-DR,

inclusive, Fig. 6, and the sending switch SEN,

Fia'. 4.

he master digit switch MDS, Fig. .5, is mechanically a simple switch having Wipers 308 and 309, which are rotated in a forward direction by the stepping magnet 338 and which are restored to normal upon the energization of release magnet 348, whose circuit is controlled through ofi' normal contacts 3L i7. The digit registers DRl-DR", inclusive, Fig. 6, are similar to the master digit switch MDS.

The sender control switch SCS, Fig. 6 is mechanically similar to the line switches DS, and to the secondary switch SLS, and its wipers are moved in a forward direction only by the stepping magnet 387 and are advanced to their normal position by the operation of the same stepping magnet.

The wipers of the sender control switch SCS are advanced upon the backward stroke of the stepping magnet 387 rather than upon the forward stroke. The sending switch SEN, Fig. 4, is similar to the mechanism of the switch SCS.

The B and C digit register BCR, Fig. 5, is a two motion vertical and rotar switch similar to the exchanve selector E The intermediate distributing frame I.D.F., Fig. 5, is individual to the director D. v

A description will first be given of the general layout of Fig. 1, showing diagrammatically automatic exchanges Nos. 1, 2 and 3, with v.director equipment, A loperators positions, at manual exchanges Nos. 2 and 3. call indicator position at manual exchange No. 1, toll operators position at the manual eX- change No. 4 and a mechanical tandem exchange MTE.

. The layout is representative without going into unnecessary complications of all calls which may be set up in a large network having oilices of the type described. It will be clear that a number of different kinds of connections may be set -u and therefore, it is proposed in the first p ace to describe a local connection in the automatic exchange N o. 1, which is to be extended from the calling party A to the wanted party A1. lVhen the calling party A removes his receiver his individual line switch LS will operate to select an idle ltrunk relay group TR with which it is then associated by means of the secondar f line switch SLS to an idle director selector S.

The calling party will first operate his calling device to send out three digits corresponding to the first three letters of the name of the automatic exchange No. 1 and then the four digits representing the wanted partys number. The director selector DS will respond to the first digit diallcd and then automatically select van idle director, such as D. The director l) will now respond to the remaining digits diallcd and send out a single ti'ain of impulses which is determined by the dialling of the first three digits corresponding to the first three letters of the wanted exchange to an exchange selector such as ES and then the digits of the wanted subscribers number. The exchange selector ES will respond to the first series of impulses sent out by the director and then automatically select an idle trunk to a first selector such as S. The director will now send out the four series of impulses corresponding to the wanted partys number. The selector S will respond to the first series and then automatically hunt for an idle second selector'such as S1 which responds ,to the second series of impulses and hunts for an idle final selector or connector, such as FS which responds to the last two series of impulses to establish connection with the line of substation A1.

A connection from the subscriber A in the automatic exchange No. 1, to the subscriber at the substation A3 in the automatic exchange No. 3 is setup in substantially'tbe same manner by the director. The callingsubscriber A will first dial the three digits representing the first three letters of the name of automatic exchange No. 3 and then four digits representing the number of the subscriber at substation A3. The first three digits recorded in the director D will now. however, be translated into a three digit office code and the first series of impulses sent. out by the director l) will operate the exchange selector E SA as before, the second series of impulses, the exchange selector` such as ES1 in the automatic exchange No. 2 and the third series of impulses, the exchange selector ES4 in the automatic exchange No. 3. It .is assumed that an 'exchange selector will be required at automatic exchange No. 3 because there is another exchange in the same build; ing` otherwise first numerical selectors inthe exchange could be connected to tl1e]nnct1on lines direct. The exchange selector E81 will respond to the second series of impulses and then automatically select an idle trunk leadand this selector will then automati ally hunt' for an idle local selector in that exchange, such as selector S2. The remaining four series ot impulses corresponding to the number of the wanted subscriber at substation A3 will new be sent out by the director and will opcrate the selectors S2. S2 and the connector FS1 to establish connection with the wanted 'pm-ty A3.

A. connection from the subscriber at substation A in-the automatic exchange No. l to the subscriber A2 in the automatic exchange No. 2 is setup in a similar manner to the previous connection, except that the director D now sends out only two seriesof 'o tlice. selecting impulses. The exchange selector ES responds to the first series of impulses and selects an idle trunk line direct to the ex change selector ES1 in the automatic exchange No. 2. The exchange selector E51 responds to the second series of impulses and this time selects a local first selector in the automatic exchange No.2 such as the selector S1, the remaining series of impulses sent outby the director corresponding to the number of 'the wanted subscriber at substation A2 and will operate the selectors S4 and S2 and connector FS2 to establish connection with the wanted part1 at substation A2. It will be noted also that in this connection no repeaters are required in the inter-exchange' trunk line between the. automatic' exchange No. l and the automatic exchange No. 2. Local connections in the automatic exchanges Nos. 2 and 3 are set up in a similar manner to the local connection between the subscribers at. suhstations A and A1 in the automatic exchange No. 1.

The subscriber at substation A1 4in the auto- Ydigits representing the ,exchangethe director sends out two series of set TR2.

at substation A in the automatic exchange N oflcan also set up a toll call by dialling the di it 0 an'd as before the director selector DS wil be raised to the tenth level whereupon special circuit changes will also take place to route the call to the manual exchange No. 4. This time however, it will be seen that the exchange selector ES in the automatic' exchange N o. l has direct access to a trunk line leading to the manual exchange N o. 4 by way of the repeater R3.

A connection from the subscriber atsubstation A in the automatic exchange No. l to the manual exchange No. 1 is set up in the following manner: 'lhe calling part).Y tirstdials the name of the wanted exchange followed by the number of the wanted party in that exchange.

Responsive tothe diallang of the lirst three name of the 'wanted impulses to select a trunk leading to the manual exchange No. 1, the iirst series operates, an exchange selector such as ES, which then automatically select-s a free trunk to a repeater such as R',it he. repeater R is ot special type so arranged that the first series of' impulses rcceived by it are repeated to a succeeding selector such as the call indicator exchange selectorCES, while subsequent series of impulses are repeated over the coder selector CS to a, coder C. Accordingly when the second series of oiiice selecting impulses are sent out by the director," the call indicator exchange selector CES will be operated and then automatically select an idle trunk line to the secondary line switch Sla 1 at the required exchange. It will be understood that the exchanges accessible to the call indicator exchange selector CES are provided with call indicating equipment. During transmission 'of the second series ot impulses to the sclectoi CES the coder selector CS will have selected an idle coder and subsequent digits transmitted by the. director will be repeated to the coder C. As soon as all the. digits have been sent the secondary line. switch SLS4 is set in operation to select anidle trunk relay In due course the trunk relay group is connected with the decoder DC and the digits recorded on the storage relays asso-- ciated with the coder C are sent out in code over the trunk line. When this process is completed the coder is released and reverts to common use and the number transmitted over the trunk line in code having been decoded at the decoder DC is displayed on'the. lalnps L at the operatorsposition O. -lThe operator then inserts a plug in the jack ot the wanted partys line, whereupon the trunk finder TF will be started up to find the trunk relay set. which has been used. Then this is found the calling party will be. rung and when he answers. the conversation proceeds in the usual manner. A detailed description of the operation of the call indicating 4apparatus in the automatic and manual exchanges is given inthe specification of British Patent 229,371. i

Connections from the manual exchange No.

' 2 to manual or automatic exchanges are set up .by the o erator at the mechanical tandem exchange TE where impulse senders IM are provided which will send ordinaryimpulses to operate selectors such as ES for selecting `the required exchange and then according as A board in the manual exchange No. 2

will besignalled in the usual manner by the subscriberat A and on learning his requirements will repeat the wanted subscribers number to the operator in the mechanical tandem exchange over an order wire. The

tandem operator will thereupon give lier the number of an idle interexchange Junction line, at the same time pressing an assignment -lrey associatedwith this line, whereupon a trunk finder such as the trunk finder TF is started to find the line in connection with which the assignment key has been pressed. When this is found the operator is notified by the lighting of a lamp and she may then set up the required number by operating the appropriete keys of her impulse sender IM. The number of the wanted subscriber at substation A. is 8332545 and of this the first three digits 833 will be used for exchange selecting purposes, and will be converted into, a single series of six impulses. The transmission of the translated and numerical portion of the wanted number will depend upon Whether the operator at the A board has plugged into the trunk assigned to her, and assuming she has done so, the first series of impulses will operate the exchange selector ES5 which Will select an idle trunk leading to the automatic exchange No. 1 the remaining series of impulses corresponding to the number of the wanted party at the substation A1 will operate the first selector S, the second selector b1 and the connector FS to complete the connection. A

If the subscriber at substation A6 desires to l,establish a connection with a subscriber.

at a call indicator exchange for instance the subscriber A7 in the manual exchange No. 1 the exchange selecting digits after being translated are transmitted in the form of impulses or operating step by step switches of the ordinary type, while the four digits corresponding to the actual subscribers number are subsequently sent out over the trunk line name and are accordingl by the exchan e selector ES in code, whereby a considera le saving of transmission time may be effected.

A full description of the apparatus and circuit arrangements in the mechanical tandem exchange is given in the specification of British Patent 229,765.

A connection from the subscriber A5 in the.

manual exchange No. 3 to the subscriber As in the automatic exchange No. 3 is setup over the A board in the manual exchange No. 3

B board in the automatic exchange No. 3, first selector such as S, second selector Ss and a final selector F S1. It will be noted that the operators at the B board in the automatic exchange only deal with calls for 'that exchange and therefore the impulse yet these include representative connectionsv of every class of connection which may be set in a very large network and connections such as the connection between manual .exchange No. 2 and the manual exchange No. 4 will be made over a more direct route than via mechanical tandem exchange MTE, and automatic exchanges Nos. 2 and 3, so as to include at most one intermediary exchange. In no case has it been found desirable to have a repeater such as R1 in serial relationship with the repeater such as R2 with the layout according to the present invention.

The apparatus having been described more or less in general, a detailed description of the operation will now be given. For this purpose it will be assumed that the subscriber at substation A, Fig. 1 desires to converse with the local subscriber at substation A.V For the purpose of illustration it will be assumed that the number of the subscriber at substation A', as listed in the directory is 8332345,the rst three digits 833 designating the desired exchange and the remaining 'four digits 2345 designating the particular substation in that exchange. It is understood that ordinarily the first three digits S33 represent the first three letters of an exchange listed in the directory as -letters instea of digits. This, however, has nothing particular to do with the invention and need not be considered further herein.

Local automtc connection..

Referrin l now to Figs. 2-8, inclusive, when the subscri er at substation A removes his receiver, line relay 6 energizes over line conductors 2 and 3 in series and earths the private normal conductor 4 at armature 16, thereby making the calling line busy to the connector switches having access to it and closing a circ; it for switching relay 5 and stepping magnet. 7 in series. Line relay G also ccnnects test wiper 10 to the junction of ielay 5 and stepping magnet 7 at armatui'e 17, and completes' the following circuit for stepping magnet 7: earth. armature 16, home position bank contact 10, wiper 10, armature 13 and its rest-ing contact, working contact and armature 17` interrupter contacts 14, stepping magnet 7 to battery. Magnet 7 thereupon rotates the wipers 8-12, inclusive, into engagement with the first bank. Assuming that the trunk terminating in the bank contacts with which wipers 8-12, inclusive, are in engagement is idle, switching relayr 5 energizes immediately in series with stepping magnet 7 and sei/.es the trunk.

In the present case it will be assumed that the tirst trunk is busy, in which case the test wiper 10 is in engagement with an earthed bank contact, and the earth potential extending to the junction of switching relay-"5 and stepping magnet 7 short circuits the former and operates the latter and the wipers 8-12, inclusive, are advanced step by step in lsearch of an idle trunk owing to the buzzer like action of stepping magnet 7 which interrupts its own circuit Yat contacts 14.

then anidle trunk is reached, ,which trunk it will be, assumed is the one comprising conductors 20-23. inclusive, switching relay 5. being no longer short circuited energizes in series with stepping magnet 7. Stepping magnet 7, however, does no t energize at this time on account of the high resistance of switching relay 5. Upon energizing switching relay 5 prepares a circuit for' the meter M at armature 15. opens the test circuit and prepares the holding circuit at armature. 13, and at armatures 18 and 19,

disconnects line conductors 2 and 3 from the windings of line relay 6 and earth respectively, and extends them by way of wipers 8 and 12. the bank contacts upon which they are. standing, conductors 2() and 23, normally closed contacts controlled by armature 24 to the windings of the line relay 25 of the trunk relay group TR. Line relay 25 thereupon energizes over the calling line and closes at armature 47, the following circuit. for line relay 48 of the exchange selector ES: battery, upper winding of relay 48. resting contactvand armature 49 of switching relay 53,

upper winding of impedance coil Gr, right ture 65 and its resting contact to the lower winding of line relay 48 and earth. Relay 48 energizes over this circuit and opens at armature 54 the circuit of the vertical mag net of the exchange selector ES.

Line relay 25 in the trunk relay group TR also completes at-armature 26 the following circuit for release relay 2": battery resistance 28, armature 26 and its working contact, relay 27 to earth. Relay 27 being provided with a copper sleeve is slightly slow to pull up as well as being slow to fall away and consequently relay 48 of the selector ES being a quick acting relay deenergizes before relay 27.Y Release relay 27, upon energizing, earths the release trunk conductor 21 at armature 29, thereby completing a holding circuit over the normally closed contacts controlled by armature 57, conductor 21, wiper 10 and armature 13 for relay 5 before the slow line relay 6 has had time to deenergize. Relay 27 at armatures 29 and 3() completes the following circuit for stepping magnet 31 of the secondary line switch SLS, Fig. 3: earth, armature 29 and its working contact, conductor 32', home position bank contact and test wiper 36, conductor 36', armature 38 and its resting contact, armature 39 and its resting contact, working contact and armature 30, resting Contact and armature 40, conductor 41, interrupter contacts and stepping magnet 31 to battery. Stepping magnet 31 energizes in this circuit and rotates the wipers 33-37, inclusive, into engagelnent with the first trunk. If this trunk is idle switching relay 42 energizes in series with stepping magnet 31 over the following circuit: earth, ainiature 7 5 and its working contact. armature 94 and its resting Contact, working contact and armature 32. resting contact and armature 93, winding of switching relay 42, conductor 41, interrupter contacts and stepping magnet 31 to battery, and seizes the trunk. 1f the first trunk to busy, test wiper 36 will be in engagement with an cart-lied bank contact, switching relay 42 will be short circuited and magnet 31 will energize and the secondary switch SLS will select an idle trunk in the manner described above for the line switch LS, which trunk is assumed to be the one comprising conductors 43-46. inclusive, and extending to the director selector DS. Fig. 3.

1When this idle trunk is reached, switching relay 42 being no longer short circuited energizes in series with stepping magnet 31, opens the test circuit and earths test wiper 36 at arniature 38; thereby earthing test conductor 44; prepares the impulsing circuit at armature 24; at armature 57 eai'ths the release trunk conductor 21 independently of armature 29 of release relay 27; at armature 58 prepares a circ-uit for stepping relay 59 of the exchange selector ES; at armature 60 opens a point in the automatic hunting circuit used for returning the secondary line switch SLS to normal position; at armature 61 prepares a circuit for supervisory relay 62; and at armature 50 and 56 completes a new loop circuit for line relay 48 of the exchange selector ES. This loop circuit includes the upper winding of relay 48, working contact and armature 49, working contact and armature 56, conductor 34', wiper 34, conductor 45, normally closed contacts controlled by armature 132, resistance r, conductor 46, wiper 35, conductor 35', armature 50 and its working contact, normally closed contacts controlled by armature 51, armature 65 and its resting contact to the lower winding of relay 48. Nothing happens responsive to the closure of this loop circuit as relay 48 was already energized over the impedance G and right hand winding of relay F. Relay F is a polarized relay of the shunt field type and only attracts its armature when both Windings are energized in the same direction for the reason that When only one winding is energized, the magnetic iiux is shunted away from the armature by the low reluctance path through the core of the associated coil. In the director selector DS, Fig. 3, the line relay energizes over the following circuit upon the operation of switching relay 42: battery feed ondial tone conductor DT, normally closed 11th step cam springs controlled by spring 102, winding of relay 103, normally closed springs controlled by armature 104, conductor 43, wiper 33, conductor 33', armature 24 and its working contact, conductor 20, wiper 8, working contact and armature 18, conductor 2, over the calling partys loop, conductor 3, armature 19 and its working contact, wiper 12, conductor 23, lower winding of relay 25 of the trunk relay group TR and earth. Relay 103 energizes over this circuit and completes a circuit for slow release rclay 105 at armature 106, whereupon relay 105 energizes and prepares the director selector DS or operation by operating its armature 107-109, inclusive.

The director selector is now in readiness to receive the iirst digit and when the calling party hears the dialling tone which is projected over the previously traced circuit for relay 103 he dials the first digit 8. lVhen the first exchange selecting digit 8 is dialled relay 25 of the trunk relay group TR and 103 of the director selector DS deenergized eight times responsive to the eight interruptions produced in their circuit by the calling device at substation A, and upon each deenergization relay 103 opens the circuit ot' slow release relay 105 at armature 106, but relay 105 being slow to release maintains its armatures attracted throughout the series of interruptions. Upon each deenergization, relay 103 closes a circuit for t-he vertical magnet 110 ofthe director selector DS as follows: from earth by way of armature 111 and its resting contact, .armature 106 and its resting contact, armature 108 and its Working contact, slow series relay 112 to the vertical ma et 110 and battery. Responsive to the eigllit impulses delivered to the vertical magnet 110 at this time the wipers 113-116, inclusive, are raised opposite to the eighth level of bank contacts. Relay 112 is energized in series with the vertical magnet 110 upon the irst impulse of current being delivered to the latter and, being slow to release, maintains its armatures 117 and 118 attracted throughout the series of impulses.

Relay 112 upon energizing, opens a pointi in the circuit of release magnet 119 at armature 118 and at armature 117 completes the following circuit for stepping relay 120: battery, relay 120, off normal springs 121 (closed on the first vertical step) armature 117 and its working contact, to the earthed release trunk conductor 44. Stepping relay 120 completes a locking circuit for itself at armature 122, and at armature 123 prepares a circuit v for t-he rotary magnet 124. It should be mentioned here that the oi normal springs 121 break on the second impulse being delivered to the vertical magnet 110 and not on the first.

This arrangement is provided to absorb or,

cancel a false or preliminary impulse by releasing the switch when only one impulse is delivered to the vertical magnet 110. The

first level of bank contacts are, of course, not

register translator equipment shown in Figs.

4 to 6, inclusive, to be idle, then the rotation of the switch will cease andthe switching relay 129 will operate.

Returning now to the transmission of the first series of impulses itwill be seen that the lower winding of relay 25 is included in the impulsing circuit., and accordingly responds simultaneously with relay 103. Relay 25 does not perform any useful function at this time other than to maintain release relay 27 energized. The object of this impulsing circuit is to save a wiper on the secondary line switch SLS, Fig. 3.

Returning now to the operation of switching relay 129 which performs the following circuit changes: at armature 130 test wiper 115 is connected to the earthed release trunk conductor 44, thus making the test contact 127 and its multiples in the banks of other director selectors busy.

This earth extends over holding conductor 200, resting contact of armature 204 of relay 205, Fig. 4, conductor 206, armature 207 and its resting contact of relay 208 to relay 209 and battery. Relay 209 at armature 210 disconnects earth from the upper bank of the sender control switch SCS, Fig. 6, and at the same armature earthsthe impulse motor starting conductor lMS; at armature 211 disconnects wiper 213 of the sending switch SEN 'from magnet 214; at armature 215 connects the common time pulse conductor TPC to the two step time relay 216; at armature 217 prepares a locking circuit :tor relay 216; at armature 218 removes earth from the chain alarm conductor CAC; at arniature 219 disconnects earth from conductor 220 and at the same armature also earths the impulse motor starting conductor IMS. The impulse motor, not shown, is `now started and drives the interrupter springs 374 which, however have no effect at this time.

Switching relay 129 at armature 104 transfers the impulse circuit from relay 103 of the director' selector DS to the impulse relay 300 of the B and C register BCR, Fig. 5, over conductor 131, wiper 114, contact 126, conductor 201 to relay 300 and battery. Belay 300 at armature 301 completesla circuit lor slow release relay 302. Belay 302 at armature 503 prepares a circuit for the vertical magnet 304 of the impulse register BCB, Fig. 5, over conductor 305, slow series relay 306, conductor 307, wiper 308 of the master digit switch MDS in first position to the Vertical magnet 304 and battery. Relay 129 at armatures 132 and 133 connects the following loop circuit across the windings of relay 48 of the exchange selector ES, Fig. 2. Battery, upper Winding of relay 48, resting contact and armature 49, resting cont-act and armature 56, conductor 34', wiper 34, conductor 45, working contact and armature 132, conductor 134, wiper 113, contact 125, conductor 202, resting contact and armature 30901 relay 314, Fig. 5, conductor 310, armature 311,` and its resting contact, conductor 312, normally closed contacts controlled by armature 313 of relay S, Fig. 6, conductor 315, let't hand winding ot' shunt field relay 316, Fig. 4, conductor 317, normally closed contacts controlled by armature 318 of relay S, conductor 319, armatures 320 and 321. in parallel, conductor 203, bank Contact 128, Fig. 3, wiper 116, conductor 135, armature 133 and its working contact, conductor 46, wiper 35, conductor 35', armature 50 and its working cont-act, Fig. 2, normally closed contacts controlled by armature 51, armature 65 and its resting contact, to the lower winding of relay 48 and earth.

Line relay 48 is maintained energized now over the above traced loop circuit extendingl through the director D.

The dialling ot the next digit 3 of the wanted number causes relay 300 of the B and C digit register BCR, Fig. 5, to transmit three impulses over the previously traced impulse circuit to vertical magnet 304 which raises the wipers 330-335, inclusive, of the register BCR opposite to the third level of bank contacts.

'Slow series relay 306 is energized in series with vertical magnet 304 and at armature 336 completes a circuit for slow relay 337. At the end of the series of inipulses' relay 306' releases and breaks tile circuit ot relay c 337, which does not release immediately and an impulse of current is transmitted to magnet 338 of: the master digit control switch MDS from earth, armature 330 and its resting contact, armature 339 and its working contact, conductor 340 to stepping magnet 338 and battery.

Magnet 338 advances wipers 308, 309 into second position and when the switch MDS leaves its normal position ofi' normal springs 347 prepare a circuit `t'or release magnet 348. Belay 306 also disconnects earth from the locking circuit ot the two step time relay 216 which is previously energized to close its cpntacts 221 over the time pulse conductor 11?() 1s deenergized, when earth is removed from conductor TPC 'by the timing device (not shown).

The two-step relay 216 is provided for-disconnecting the director in case the calling party should fail to dial the complete number, and in the ordinary operation of the system this relay is not fully operated.

The dialling of the next digit 3 causes relay 300 to transmit three impulses over wiperI 308 of switch MDS in second position, conductor 341 to the rotary magnet 342 of the impulse register BCB.

'lhe normal post springs NPS are provided for use in 2 digit code systems only. ln 3 digit code systems the rotary magnet 342 is wired direct to the second contact in the bank ot wiper 308 ot the switch MDS.

During the rotary movement relays 306 and 337, Fig. 4, energize and at the end ot the rotary movement deenergize and transmit another impulse ot current to magnet 338 of switch MDS, which advances its wipers to third position. lViper 308 is now connected to magnet of the thousands digit register DB, and wiper 309 connects earth to the starting conductor 400. The earth on conductor 400 causes the sending switch SEN to transmit impulses in accordance with the exchange code which has been determined by the dialling of the first three digits 833 of the wanted number, and it is thought best at this stage to defer the explanation of these operations and to describe the operation ot the register switches DB1, DB2, DB,3 and DB4 in registering the four digits 2, 3. 4, 5 of' the wanted number. The dialling of the thousands digit 2 causes impulse relay 300 to transmit two impulses to magnet 343 of the thousands register DB1, Fig. 6, over con-A ductor 343 which advances wiper 344 two steps. When the register DB1 leaves its normal position o normal springs 345 prepare a circuit for release magnet 346.

'Slow relay 306 is energized in series with magnet 343 and in conjunction with relay 337 transmits another impulse to magnet 338 of switch MDS which advances Wipers 308 and 309 to fourth position. Wiper 308 in moving from' third to fourth position, transfers the control circuit from magnet 343 to magnet 349. No circuitl changes are brought about by the further movement of wiper 309, since contacts 3 to 10, inclusive, are multipled together.

When the hundreds digit 3 is dialled, relay 300transmits three impulses over relay 306 and conductor 349 to magnet 349 of the hundreds register DB2, which advances wiper 350 into engagement with the third contact in the bank of register DR?. When the register DR2 leaves its normal position off normal springs 351 prepare a circuit for release magnet 352 and 0H normal springs 353 prepare a circuit for earthing conductor 401. At the end of this series of impulses slow relays 306 and 337 transmit an impulse of current to magnet-338 and switch MDS which advances wipers308 and 309 to fifth position. In a similar manner to the above, when the calling party dials the tens digit 4 and the units digit 5, a series of four impulses is transmittedto magnet 338 of the tens register DB3, and a series 'of verimpulses is then transmitted to magnet 359 of the units register DR.r

Referring now to Fig. 4, the sending switch SEN is started by wiper 309 of switch MDS in third position connecting earth to starting conductor 400. The code in accordance with which the call is trunked to the local exchange is one series of three impulses as will be seen from the trunking layout, Fig, 1, and accordingly the third set of contacts in the third level of the register switch BCR, which were selected by dialling the digits 833, is so cross connected at the IDF as to cause the transmission of one series of impulses. This is effected at the IDF by connecting terminal 1 on the right hand side of the IDF to terminal 3 on the left hand sid'e and terminals 2, 3, 4, 5 and 6 on the lefthand side to terminal DGO on the left hand side by so called jumper wires. Starting conductor 400 extends to the sender control switch SCS, Fig. 6, where it is connected to the first six contacts in the bank of wiper 364 and to wiper 365. Accordingly earth is connected to the No. 3 contact in. the bank of stop wiper 230 of the sendingJ switch SEN, Fig. 4, over conductor 400, Wiper 365 in normal position, conductor 392, wiper 330, terminal No. 1 on the right hand side of the IDF to terminal No. 3 on the left hand side, conductor 367, to the No. 3 contact in the back of stop wiper 230 of the sending switch SEN. f

At the same time a circuit is completed for the two-step starting relay 373 of the sending switch SEN as follows: earthed conductor 400, wiper 364 of switch SCS, Fig. 6, in first position, conductor 401, interrupter springs 374 on common driving motor, armatures 375, armature 376, armature 377 and their back contacts to the upper windlng of two step relay 373 and battery. Relay 373 is marginally adjusted and only operates armature 37 8 in this circuit. Armature 378, however, connects the upper and lower windings of relay 373 in series and it fully operatesover the following circuit when the interrupter springs 374 are opened: battery, upper and lower windings of relay 378 in series, working contact and armature 37 8', resting contact and armature 379, conductor 380, armature 381 and its working contact of relay 302, Fig. 5, to earth. Relay 3F 3 upon attracting its armatures 377 places the stepping magnet 214 ofthe sending switch SEN under the control of interrupter springs 374. Stepping magnet 214 energizes upon the closure of the interrupter springs 374 and opens the impulsing cont-acts 321, which, however, are short circuited by armature 320 and` its resting contact of slow relay 378. Upon the opening of interrupter springs 374 magnet 214 deencrgizes and wipers 213 and 230 are advanced one step in which position stop wiper 230 engages a dead contact and wiper 213 and earthed contact. The latter completes a circuit for slow relay 378 which energizes and prepares a locking circuit for stop relay 381 at armature 380 and removes the short circuit from impulsing contacts 321 at armature 320. The second time interrupter springs 374 open the circuit of magnet 214 the wipers 213 and 230 are advanced one more step, thus bringing the stop wiper 230 into engagement with the N o. 1 contact in its bank, and also, since relay 37 8 is now energized magnet 214 opens at the impulsing contacts 321 the circuit of line relay 48 of the exchange selector ES, Fig. 2.

The energizations and deenergizations of magnet 214 continue in quick succession under the control of the interruptor springs 37 4 until stop wiper 230 is advanced into engagement with the No. 3 contact, which is ealthed at this time over conductor 367 and a circuit is completed for stop relay 381 which ter1ninates the office code digit 3. Relay 381 closes at armature 382 a locking circuit for itself. at armature 376 opens the circuit of stepping magnet 214, at 379 opens the circuit of two step start relay 373, at armature 383 short circuits the impulsing contacts 321 so as to prevent their subsequent operation interfering with the switch control circuit and at 384 completes a local circuit for stepping n'iagnet 214 including its over interrupter contacts 385 and wiper 213. By the closure of the lat- 

